Water craft having ventilated propeller

ABSTRACT

Improvement in water craft of single-hull type or multi-hull type and having a drive apparatus or a hub ( 7 ) carrying a ventilated propeller ( 6 ) of so called “surface piercing” type, in which the drive or the hub ( 7 ) with the surface piercing propeller ( 6 ) is mounted close to the end of a fin like hull body ( 4 ), or a fin like part of an integral hull body, preferably having an elongated torpedo like ( 11 ) bottom body, and which fin like body ( 4 ) is so deep that the propeller ( 6 ), at all speeds of the ship, operates entirely under water, and in which the rear end of the conical fin body ( 4, 11 ) extends transversally to the longitudinal direction of the ship and has an average width in this direction which is substantially less than the diameter of the propeller ( 6 ). The torpedo like body ( 11 ) may have a front cone which can be expelled some distance in front of the torpedo body ( 11 ).

FIELD OF THE INVENTION

The present invention relates to an improvement in water craft ofsingle-hull type or multi-hull type and equipped with one or moreventilated propellers of so called “surface piercing propeller” type,especially water craft intended to be driven at high speeds over water,for instance speeds of at least 20-30 knots, preferably up to 50 knotsor more.

BACKGROUND OF THE INVENTION

Normally propellers of surface piercing propeller type are arranged andmounted so that the propeller, upon driving the boat in a water surfaceplaning position, operates with at least 50% of the driving surfaceabove the sea water surface or otherwise in a corresponding gas or airflow. Propellers of this type exhibit many advantages over conventionalpropeller arrangements, where the propeller as a complete operates underwater. Among other things, the fact that the propeller in part operatesin the air involves the advantage that there will be very little, ifany, cavitation, and that the propeller, in spite exhibiting very strongpropulsion force, is subjected to very small, if any, cavitationdamages.

In some respects, however, a surface piercing propeller also can giverise to some problems. Since the propeller blades to a great part oftheir revolution operates in air there will appear a lifting force whenthe propeller, after having rotated in the air, hits the water surface.The propeller blades thereby hit the water surface with a substantiallyhorizontal force. Said lifting force can amount even up to 30% of thepropulsion force of the propeller, and this will reduce the effectivepropulsion ability of the propeller.

Since only half the propeller operates under water the impact force ofthe propeller against the water surface also will make the propellershaft be subjected to a certain unevenly distributed load which maycause problems with wear of bearings, vibrations, and in the worst case,rupture of the propeller shaft.

There has been a desire to make it possible to make use of thefavourable properties of surface piercing propellers by using suchsurface piercing propellers also for propulsing ships in the cases wherethe propeller, even at full speed of the ship, operates entirely underwater. This, however, has not met with success depending on a problemwhich has been difficult to solve:

Since the propeller operates entirely under the water surface there willbe a strong sub pressure against the surface of the propeller facingforwardly and this leads to cavitation and cavitation damages dependingtherefrom. Cavitation damages can generally be compared with corrosiondamages. For eliminating such problem it is necessary that the surfacepiercing propellers are ventilated, so that the sub pressure againstfront surfaces of the propeller blades can be unloaded at eachindividual revolution of the propeller, and whereby air bubbles, whichtend to appear at the (front) suction side of the propeller in case ofcavitation, are removed. The ventilation also should be such that thepropeller blades, during the greatest part of their revolution, forinstance up to 90% of their revolution, are allowed to operate in thewater, whereas said propeller blades, during a very little part is itsrevolution, operate in the air. In this last mentioned case the subpressure on the suction side of the propeller blade is unloaded, andthis strongly reduces the risk of appearance of cavitation.

The ventilation of a surface piercing propeller, which operates entirelyunder water has, in turn, caused special problems.

SUMMARY OF THE INVENTION

According to the invention the drive, or the hub of the water craft,with the surface piercing propeller is mounted adjacent the bottom of afin like hull body, or a part of a complete hull body comprising a finlike hull part extending down towards the propeller hub, and wherebysaid hull part has a rear side extending transversally to thelongitudinal direction of the water craft and has an average width insaid direction which is substantially less than the propeller diameter.In the vertical direction the transversely cut conical fin body shouldextend at an angle upwards-forwards from the propeller centre of notmore than 45° to an angle upwards-rearwards from the propeller of notmore than 45°. While propulsing the water craft forwards at a medium tohigh speed the fin like hull part creates a cone shaped air column downto the propeller hub, and behind the propeller a successively reducedcone shaped air chamber. Said air column down to the propeller centreshould be as narrow as possible, and preferably it should not cover morethan 10% of the propulsion surface of the propeller, at a maximum. It isvery important that said air column at the propeller hub is so narrow aspossible. When the propeller rotates each propeller blade passes onceper revolution through said air column, whereby the sub pressure againstthe propeller blade is practically completely unloaded.

Tests in water have proved that a water craft of the described typehaving a surface piercing propeller and having the above describedV-shaped hull fin does not give such cavitation sling of air which isnormally seen after conventional water craft having sub-water drivenpropellers giving a high propulsion force.

Both sides of the fin like sub water body or hull body portionpreferably are concave and can have such arc shape that the tangent ofthe sides of the fin body adjacent the propeller hub is 0°, that is thatsaid sides extend in the vertical direction. An angle between thepropeller centre and the contact point of the hull body with the seawater surface, when the water craft is running at medium to high speed,can for instance be ±45°, at a maximum.

In a special embodiment of the invention the drive or hub is formed likea type of torpedo having a circular cross section, which torpedo has, atits rear end, a propeller, and the length of which is about 10-20 timesthe greatest diameter thereof, most preferably about 12-16 times thetorpedo diameter. The front end of the fin with the torpedo portion canpreferably meet the ordinary hull body portion in the form of a clipperstem like part, that is in a kind of C-formation.

In a still further preferred embodiment of the invention the torpedolike body mounted under the ordinary hull of the water craft is formedas a housing for the drive engine, for instance the gas turbine, andpossibly also for the fuel tank, whereby the centre of gravity of thewater craft will be placed lower than is possible in ordinary watercraft, in which the drive engine is normally mounted inside the hullabove, or at least close, to the sea water level. Therefore the torpedowith the engine acts as a type of heavy keel for the water craft.

A further advantage with the such an apparatus also is that thepropeller can be mounted with the propeller shaft extendinghorizontally, meaning parallelly the sea water level when the watercraft is running at cruising speed. This gives an optimum goodpropulsion ability, in particular since the propeller can be mountedwith the thrust surfaces thereof at an optimum angle in relation to thesea and the running, water craft.

In a still further embodiment of the invention the front end of thetorpedo like submarine body, which is opposite to the propeller end, isformed with a streamline cone which can be extended some distancethereby forming an annular space between the torpedo body and the frontcone, in which annular space air band/or exhaust gases from the driveengine can be pressed out, which air forms an air jacket round thetorpedo body, which air jacket extends as far as to, and past thepropeller thereby ventilating same. By expelling the front cone more orless in relation to the torpedo body there is obtained a more narrow ormore widened air/gas jacket. Thereby the ventilation of the propellercan be adjusted to an optimum, adapted to different speeds and/ofdifferent loading ot the water craft.

Thus, the invention relates to an improvement in water craft ofsingle-hull or multi-hull type and having a ventilated propeller of socalled “surface piercing propeller” type, in particular water craftintended to run at high speeds in the sea,

which makes it possible to use a surface piercing propeller in spitethat the entire propeller is located underneath the water surface,

in which the propeller introduces a minimum lifting force during itsrotation, and in which the propeller only introduces a side force whichcan be made neglectible, or can even be nil, and can be inhibited byusing twin mounted propellers,

which is formed with a downwards tapering fin like hull portion, or akeel type body, arranged to create an air column down to, or round thepropeller hub and which provides an unloading of the sub pressureagainst the propeller blades for each single revolution thereof,

which is formed so that the propeller shaft can be mounted with the axisthereof extending horizontally, AND

which is formed so that the can be created a differently extensive flowor air or gas past the propeller.

Further characteristics and advantages of the invention will be evidentfrom the following detailed specification in which reference will bemade to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings FIG. 1 is a diagrammatic perspective view obliquely frombehind of a water craft according to the invention having a specialbottom shape.

FIG. 2 is a side view of a little portion of the stern of the watercraft according to FIG. 1, and

FIG. 3 shows the same water craft straight from behind.

FIG. 4 shows an alternative embodiment of a fin like hull part accordingto the invention in a catamaran type water craft, seen obliquely frombehind, and

FIG. 5 diagrammatically illustrates the function of the ventilation ofthe propeller in four successive projections.

FIG. 6 shows a boat of single hull type formed with a fin like accessorypart according to the invention.

FIG. 7 correspondingly shows the invention applied to a catamaran type“Surface Effect Ship”(SES-ship), and

FIG. 8 shows the invention mounted on a trimaran type ship.

FIG. 9 is a side view of a part of a hull including a torpedo like hullpart belonging to a water craft according to the invention.

FIG. 10 shows an alternative embodiment of a torpedo like hullextension, and

FIGS. 11 and 12 shows the function of the torpedo extention according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIGS. 1, 2 and 3 there are shown a water craft having a speciallydesigned bottom, which is arranged to make it possible to ventilatepropellers of surface piercing type. The water craft, which, in thiscase, is shown as a catamaran hull, has a superstructure 1, a port sidehull 2 and a starboard hull 3. At the bottom surface of each hull 2, 3there is a type of fin body 4 which, in the illustrated case, hassubstantially plain parallel sides. The flat stern 5 of the ship iscross cut perpendicularly to the longitudinal direction of the ship andit is substantially vertical. At the bottom of each hull there is showna propeller 6 which is beared in a hub or in a drive housing 7. Thepropeller operates entirely underneath the water surface 8 at all speedsof the water craft (ship).

Depending on this shape of hull 2, 3 and stern 5 there is formed such aflow of water past the propeller 6 that air is sucked down towards thecentre of the propeller 6 in a narrow, column like air flow 9 asindicated in FIGS. 2 and 3. The flow of air can form a slightly conicalangle downwards having such length in the longitudinal direction of theship that each propeller blade passes the air flow in its uppermostposition, preferably in a sector of the rotation circle of 5-30°. Inmany cases it is considered a disadvantage that air is sucked down tothe propeller, but for so called “surface piercing propellers” this is,on the contrary, a great advantage. For surface piercing propellers itis necessary that the propeller is ventilated. Therefore the bottomstructure of the hull should be such that the, or each propeller isventilated in a sector s, see FIG. 3, of for instance 5-30° of therotation circle of the propeller, and this is provided in that the hullis formed with a lower fin 4, in that the ship has a flat, substantiallyvertical, or up to ±45° inclined stern 5, and in that the propeller, atcruising speed and higher speeds of the water craft, is located on apredetermined level underneath the sea water level, which level isreached by the downwards-rearwards sucked flow of air, and which remainson a predetermined distance rearwards of the stern.

In FIG. 4 is shown a hull fin 4 which can be made integral with thehull, or which can be formed as a separate unit which is mounted againstthe bottom of an available water craft. The fin is formed as a fin bodywhich tapers downwards in a bow form. The fin is so deep that thepropeller operates entirely under the sea water level 8, even at mediumhigh to very high speeds of the ship. The average width of the fin issubstantially less than the diameter of the propeller 6. The tangent ofthe bow formed fin side 10 becomes less in the direction downwards andapproaches, or is equal to 0° at the propeller hub 7, in other words sothat the said tangent is thereby vertical. The angle between thepropeller centre and the points where the fin sides 10 meet the seawater surface 8 may vary from about ±10° to about ±45°, as calculatedfrom a vertical line through the propeller centre. Also in theembodiment shown in FIGS. 4 and 5 the stern of said fins extendsperpendicularly to the longitudinal direction of the ship. In thevertical direction said stern can extend vertically.

As indicated in FIG. 9 the stern of the fin 4 may, however, extend at anangle V1 upwards-forwards from the propeller hub 7 of up to 45°. It isalso possible to make the stem 5 extend upwards-rearwards at an angle V2of up to 45°, supposing there is free space for the propeller to rotate.

The fin 4 should have its smallest width adjacent the hub 7. For bestfunction the hub is extended forwardly to form a torpedo like body 11,which torpedo body is elongated in the forward direction a distancecorresponding to 10-20 times, or preferably 12-16 times the diameter ofthe torpedo body. The torpedo body 11 is levelled in the longitudinaldirection of the water craft (ship) so as to be parallel to the seawater level 8 at cruising speed, and up to full speed, forwards of thewater craft. The torpedo body 11 may have such streamline as to give anoptimum little water flow resistance. At the front end the fin meets andis connected to the ship hull in a clipper stem like formation or aC-formation 12.

When the ship is moved at medium to high speeds a column of air 9 issucked down towards the propeller and the propeller hub 7. The aircolumn ought to be as narrow as possible in order not to unnecessarilyreduce the propulsion capacity of the propeller(s). Even a very narrowair column 9 provides the intended ventilation and unloading of the subpressure of the propeller blades when said blades rotate past the aircolumn. The air column 9 leaves an air shadow 13, see FIG. 5, behind theship which is moving forwardly, which air shadow is successivelydiminished and finally disappears behind the moving ship. With the shapeof the fin 4 and the torpedo body 11, as shown in FIGS. 4 and 5, the airshadow has the shape of key hole turned upside down, as diagrammaticallyindicated in four hatched projections in FIG. 5.

When the propeller rotates each propeller blade operates, during thegreatest part of its revolution, in water, preferably to more than 90%of its revolution. During the operation in water there is developed asuccessively increased pressure force against the rearwardly facing sideof the propeller blade, and correspondingly there is created asuccessively increased sub pressure against the forwardly facing side ofthe propeller blades, that is against the suction side of the propellerblades. Such sub pressure should cause cavitation if there was noventilation of the propeller, as shown with the air column 9, but assoon as the propeller blade enters the air column 9 said sub pressureagainst the propeller blade is unloaded. When the propeller bladethereafter enters the water aside of the air column a sub pressure onceagain starts building up on the forwardly facing side, the suction side,of the propeller blade, and correspondingly a cycle of sub pressure andunloading of such sub pressure is repeated.

When the propeller blade, after having passed the air column 9, step bystep enters the water there is obtained a certain pressure in thetransversal direction. Such side pressure is of neglectible strength anddoes not significantly influence the propulsion ability of thepropeller, especially not in case the water craft is formed with twinmounted, counter rotating propellers.

The drive arrangement including the ventilated propeller arrangement andthe fin like body 4 can be formed as an integral part of the ship hull,but it can, alternatively, also be formed as a separate unit which ismounted against the bottom of a hull or a hull part.

In FIG. 6 there is shown a single-hull boat equipped with a drivearrangement according to the invention having a fin type keel 4 and asurface piercing propeller 6. In the illustrated case the entire fintype drive arrangement is formed as a separate unit which, in anysuitable way, is secured to the boat hull.

FIG. 7 shows a catamaran (quadramaran) of Surface Effect Ship (SES) typein which each of the two intermediate hulls 16 is formed with a surfacepiercing propeller 6, and in which, at cruising speed of the watercraft, there is formed an air filled side keel chamber 18 between eachpair of an intermediate hull 16 and the outer hull 17, which side keelchamber 18 acts as a type of air support cushion which carries andstabilises the ship when moved at medium to high speed.

FIG. 8 shows a rather conventional trimaran which is formed with threefin bodies 4 and belonging torpedo bodies and is formed with surfacepiercing propellers 6.

In FIG. 9 there is shown a water craft according to the invention, seenin a side view. It is evident that the fin body 4 extends horizontally.By the bow formed (sinus formed) lines 19 behind the propeller isindicated the propeller movement in the sea water. It is also indicatedthat the drive engine 14 can be mounted at any suitable place in theordinary hull and can transmit the engine power to the propeller via enangle shaft 15, electrically or hydraulically, the end part of whichconnected to the propeller 6 is substantially horizontal.

In FIGS. 10-12 there is shown a still further preferred embodiment ofthe invention, in which the torpedo like body mounted under the ordinaryhull of the water craft is formed as a housing for the drive engine 14,for instance the gas turbine, and possibly also for the fuel tank,whereby the centre of gravity of the water craft will be placed lowerthan is possible in ordinary water craft, in which the drive engine isnormally mounted inside the hull 1 above, or at least close, to the seawater level 8. Therefore the torpedo with the engine acts as a type ofgravity force keel for the water craft.

A further advantage with the such an apparatus also is that thepropeller 6 can be mounted with the propeller shaft 20 extendinghorizontally, meaning parallelly the sea water level 8 when the watercraft is running at cruising speed. This gives an optimum goodpropulsion ability, in particular since the propeller can be mountedwith the thrust surfaces thereof at an optimum angle in relation to thesea and the running water craft.

In a still further embodiment of the invention the front end of thetorpedo like submarine body 11, which is opposite to the propeller end,is formed with a streamline cone 21 providing an optimum water flow pastthe submarine body. In an embodiment of the invention said front cone 21is formed and connected to the torpedo body 11 so that it can beextended some distance thereby forming an annular space 22 between thetorpedo body 11 and the front cone 21, in which annular space air and/orexhaust gases 23 from the drive engine can be pressed out, which airforms an air jacket 24 a, resp. 24 b round the torpedo body 11, whichair jacket extends as far as to, and past the propeller 6 therebyventilating same. By expelling front cone 21 more or less in relation tothe torpedo body there is obtained a more narrow 24 a or more widenedair/gas jacket 24 b. Thereby the ventilation of the propeller can beadjusted to an optimum, adapted to different speeds and/of differentloading ot the water craft.

REFERENCE NUMERALS 1 superstructure 2 hull 3 hull 4 fin 5 stern 6propeller 7 hub 8 water level 9 air flow 10 fin side 11 torpedo body 12clipper type stem 13 air shadow 14 engine 15 angle shaft 16 intermediatehull 17 outer hull 18 side keel chamber 19 sinus lines (propeller) 20propeller shaft 21 cone 22 annular space 23 air, exhaust gases 24 airspace (24a, 24b)

What is claimed is:
 1. A water craft having at least one hull and adrive apparatus carrying a ventilated propeller, the drive apparatusbeing mounted close to the end of a fin like hull body, the fin likehull body extending along a substantial part of the water craft andbeing sufficiently deep that the propeller, at all speeds of the craft,operates entirely under water level, the fin like hull body extending ina transverse direction to a longitudinal direction of the craft andhaving an average width in the transverse direction substantially lessthan a diameter of the propeller and wherein the drive apparatus hassmaller diameter than a width of the fin like hull body at the upperedge of the drive apparatus, and wherein a drive body is extended toform an elongated streamline torpedo like body.
 2. A water craftaccording to claim 1, wherein a rear end of the fin like hull body iscross cut and extends vertically upwards.
 3. A water craft according toclaim 1, wherein the fin like hull body has concave sides, the tangentsof said concave sides, at the drive apparatus, being as low as 0°.
 4. Awater craft according to claim 3, wherein the shape of the fin like hullbody is such that the angle between a center of the propeller and apoint where a set of concave sides of the fin like hull body meet thewater surface is not more than 45° as seen in both directions from avertical line through the propeller center.
 5. A water craft accordingto claim 1, wherein the drive body is 10-20 times longer than thegreatest diameter thereof.
 6. A water craft according to claim 5 whereinthe drive body is 12-16 times longer than the greatest diameter thereof.7. A water craft according to claim 1, wherein the fin like hull body,at a front end thereof, meets a bottom of a main hull of the ship in aclipper stem formation.
 8. A water craft according to claim 1, whereinthe drive body is mounted so as to extend substantially parallel to thewater level when the water craft is moving at cruising speed, andwherein the drive body includes at the front end, a streamline cone. 9.A water craft according to claim 8, wherein the streamline cone ismounted so that it can be extended some distance forwards from the drivebody thereby providing an annular space between the drive body and thestreamline cone, air or exhaust gases being pressed out in the annularspace the air or exhaust gases forming an air jacket along the drivebody and past the propeller of the moving water craft.
 10. A water craftaccording to claim 1, wherein the drive body carries a drive engine andthe fulel tank for said drive engine.
 11. A water craft according toclaim 10, wherein the drive engine is mounted so as to be connected tothe propeller over a straight propeller shaft extending substantiallyparallel to the water level at cruising speed of the water craft.
 12. Awater craft according to claim 1, wherein the fin like hull bodycomprises a separate unit arranged to be mounted to the bottom of asingle hull boat.
 13. A water craft according to claim 1 wherein the finlike hull part has a conical shape.
 14. A water craft according to claim13, wherein the shape of the fin like hull body and the suction actionof the propeller act in conjunction to form a conical air column alongthe exterior of the water craft hull to the propeller when the craft ismoved at medium to high speed, and wherein a successively reducedconical air chamber is formed behind the propeller.
 15. A water craftaccording to claim 14 wherein the fin like hull body is formed so thatthe air column is sufficiently narrow, so as to occupy a surface area ofno greater than 10% of the revolution surface of the propeller.
 16. Awater craft according to claim 1 wherein the drive apparatus comprises apropeller hub.
 17. A water craft according to claim 1 wherein a rear endof the fin like hull body extends at an angle upwards-forwards from thepropeller of not more than 45° to an angle upwards-rearwards from thepropeller of not more than 45°.
 18. A water craft according to claim 1,wherein the fin like hull body comprises a separate unit arranged to bemounted against each hull of a multi hull ship.
 19. A water craft havingat least one hull and a drive carrying a ventilated propeller, the drivebeing mounted close to the end of a fin like hull body, the fin likehull body extending along a substantial part of the water craft andbeing sufficiently deep that the propeller, at all speeds of the craft,operates entirely under water level, the fin like hull body extending ina transverse direction to a longitudinal direction of the craft andhaving an average width in the transverse direction substantially lessthan a diameter of the propeller, and wherein the fin like hull body hasconcave sides, the tangents of said concave sides, at the driveapparatus, being as low as 0°.
 20. A water craft having at least onehull and a drive apparatus carrying a ventilated propeller, the driveapparatus being mounted close to the end of a fin like hull body, thefin like hull body extending along a substantial part of the water craftand being sufficiently deep that the propeller, at all speeds of thecraft, operates entirely under water level, the fin like hull bodyextending in a transverse direction to a longitudinal direction of thecraft and having an average width in the transverse directionsubstantially less than a diameter of the propeller, and wherein thedrive apparatus comprises a propeller hub.
 21. A water craft having atleast one hull and a drive apparatus carrying a ventilated propeller,the drive apparatus being mounted close to the end of a fin like hullbody, the fin like hull body extending along a substantial part of thewater craft and being sufficiently deep that the propeller, at allspeeds of the craft, operates entirely under water level, the fin likehull body extending in a transverse direction to a longitudinaldirection of the craft and having an average width in the transversedirection substantially less than a diameter of the propeller, andwherein a rear end of the fin like hull body extends at an angleupwards-forwards from the propeller of not more than 45° to an angleupwards-rearwards from the propeller of not more than 45°.